Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of physical and media access control (MAC) specifications for implementing wireless local area network (WLAN) communications between a set of network devices, referred to as stations, and/or access points. These specifications provide the basis for wireless network products using the Wi-Fi brand managed and defined by the Wi-Fi Alliance. The specifications define the use of the 2.400-2.500 GHz as well as the 4.915-5.825 GHz bands. These spectrum bands are commonly referred to as the 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channels with a center frequency and bandwidth. The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, though some countries regulate the availability of these channels. The 5 GHz band is more heavily regulated than the 2.4 GHz band and the spacing of channels varies across the spectrum with a minimum of a 5 MHz spacing dependent on the regulations of the respective country or territory.
Communication, on any given channel of either the 2.4 GHz or the 5 GHz band, between network elements of the WLAN utilizes the clear channel assessment (CCA) protocol. CCA is defined in the IEEE 802.11 standard as part of the Physical Medium Dependent (PMD) and Physical Layer Convergence Protocol (PLCP) layer. Clear Channel Assessment is composed of two related functions, carrier sense (CS) and energy detection (ED). The CCA protocol is implemented in the physical layer (PHY) of a network device and determines the current state of use of the wireless medium (WM) (i.e., a 2.4 GHz or 5 GHz band), such that a network device (e.g., a station) will access a channel of the WM only when the WM becomes idle.
The conventional CCA rule mechanism defined in IEEE 802.11 defines the primary channel to be busy, if one of the conditions listed in the Table I is met, otherwise the primary channel is considered to be idle. If the primary channel is idle, the PHY will check the secondary channels.
TABLE IOperating Channel WidthConditions20 MHz, 40 MHz, 80 MHz,The start of a 20 MHz NON_HT PPDU160 MHz or 80 + 80 MHzin the primary 20 MHz channel asdefined in 18.3.10.6 (CCA requirements)40 MHz, 80 MHz, 160 MHzThe start of a 40 MHz non-HT duplicateor 80 + 80 MHzor VHT PPDU in the primary 40 MHzchannel at or above −79 dBm,The start of an HT PPDU under theconditions defined in 20.3.21.5 (CCAsensitivity)80 MHz, 160 MHz orThe start of an 80 MHz non-HT duplicate80 + 80 MHzor VHT PPDU in the primary 80 MHzchannel at or above −76 dBm60 MHz or 80 + 80 MHzThe start of a 160 MHz or 80 + 80 MHznon-HT duplicate or VHT PPDU at orabove −73 dBm